The development of highly absorbent members for use as disposable diapers, adult incontinence pads and briefs, and catamenial products such as sanitary napkins, is the subject of substantial commercial interest. A highly desired characteristic for such products is thinness. Thinner products are less bulky to wear, fit better under clothing, and are less noticeable. They are also more compact in the package, making the products easier for the consumer to carry and store. Smaller products allow reduced distribution costs for the manufacturer and distributor, require less shelf space required in the store per diaper unit, and require less packaging material.
The ability to provide thinner absorbent articles such as diapers is contingent on the ability to develop relatively thin absorbent cores or structures that can acquire and store large quantities of discharged body fluids such as urine or menses. In this regard, the use of certain absorbent polymers often referred to as xe2x80x9chydrogels,xe2x80x9d xe2x80x9csuperabsorbentsxe2x80x9d or xe2x80x9chydrocolloidxe2x80x9d material has been particularly important. See, for example, U.S. Pat. No. 3,699,103 (Harper et al.), issued Jun. 13, 1972, and U.S. Pat. No. 3,770,731 (Harmon), issued Jun. 20, 1972, that disclose the use of such absorbent polymers (hereafter xe2x80x9chydrogel-forming absorbent polymersxe2x80x9d, or HFAPs) in absorbent articles. Indeed, the development of thinner products has been the direct consequence of thinner absorbent cores that take advantage of the ability of these hydrogel-forming absorbent polymers to absorb large quantities of discharged body fluids, typically when used in combination with a fibrous matrix as compared with a fibrous matrix alone. See, for example, U.S. Pat. No. 4,673,402 (Weisman et al.), issued Jun. 16, 1987 and U.S. Pat. No. 4,935,022 (Lash et al.), issued Jun. 19, 1990, that disclose dual-layer core structures comprising a fibrous matrix and hydrogel-forming absorbent polymers useful in fashioning thin, compact, products.
Significant prior art describes absorbent structures having relatively low amounts (e.g., less than about 50% by weight) of these hydrogel-forming absorbent polymers. See, for example, U.S. Pat. No. 4,834,735 (Alemany et al.), issued May 30, 1989 (preferably from about 9 to about 50% hydrogel-forming absorbent polymer in the fibrous matrix). There are several reasons for this. The hydrogel-forming absorbent polymers employed in prior absorbent structures have generally not had an absorption rate that would allow them to quickly absorb body fluids, especially in xe2x80x9cgushxe2x80x9d situations. This has necessitated the inclusion of fibers, typically wood pulp fibers, to serve as temporary reservoirs to hold the discharged fluids until absorbed by the hydrogel-forming absorbent polymer. This fluid is not tightly held in storage cores and can be expressed by pressure or capillary contact back onto the skin of the wearer, resulting in undesirable skin wetness. In order to maintain skin dryness, such fluid must be gelled quickly and completely. Also, cores made with relatively low concentrations of HFAP are inherently relatively thick and bulky.
HFAPs are often made by polymerizing unsaturated carboxylic acids or derivatives thereof, such as acrylic acid or its salt with low levels of crosslinking monomers, typically di- or poly-functional monomer materials such as N, Nxe2x80x2-methylenebisacrylamide, trimethylol propane triacrylate, or triallyl amine. The presence of crosslinking monomers renders these polymers water-insoluble, yet water-swellable. Higher levels of cross-linking increase gel strength while reducing gel volumes. Gel strength relates to the tendency of the hydrogel formed from these polymers to deform or xe2x80x9cflowxe2x80x9d under an applied stress. Gel strength needs to be such that the hydrogel formed does not deform and fill to an unacceptable degree the capillary void spaces in the absorbent structure or article, a phenomenon called xe2x80x9cgel blockingxe2x80x9d. This would otherwise reduce the rate of absorption and the fluid distribution throughout the structure/article. Various designs have been advocated for reducing or preventing gel blocking, some of which require use of added fibrous material which tends to increase the thickness of the product undesirably. See, for example, U.S. Pat. No. 4,654,039 (Brandt et al.), issued Mar. 31, 1987 (reissued Apr. 19, 1988 as U.S. Reissue Pat. No. 32,649), U.S. Pat. No. 4,834,735 (Alemany et al.), issued May 30, 1989. U.S. Pat. No. 5,652,646 (Goldman et al.), issued Oct. 8, 1996, describes use of HFAPs which have both high porosity and high strength in high concentration cores. This patent therefore addresses the problem of gel blocking in high concentration HFAP regions by using HFAPs that retain porosity such that additional fibers are not necessary.
The effective rate at which these hydrogel-forming polymers will gel in the presence of body fluids (e.g., urine) is also important. A typical current hydrogel-forming polymer will gel completely when exposed to excess aqueous fluids such as urine over a period of about 5-20 minutes.
The rate of gellation of HFAPs in aqueous fluids has been measured by several techniques. The vortex method described in U.S. Pat. No. 5,601,542 involves addition of HFAP to a stirring aqueous solution and measuring the time required for the solution to seize and stop stirring. This patent describes absorbent cores having concentrations of HFAP of 30-100% which also have a Pressure Absorbency Index (PAI) (a value said to relate to insensitivity to pressure, infra) of at least 120 and extractables levels of less than about 13 wt. percent. Claim 29 of this patent describes similar high concentration cores made with HFAPS having a PAI of at least 120 and a vortex time of less than about 45 seconds.
The Free Swell Rate (FSR) method described in U.S. Pat. No. 5,149,335 (Kellenberger et al.) issued Sep. 22, 1992 involves determination of the time required for 1.0 g of HFAP to imbibe 20 mL of test fluid.
Yet another method involves microscopic examination of the HFAP in the gelling solution and measuring the dimensions at specific time intervals (Tanaka, T.; Fillmore, D. J. J. Chem. Phys., 1979, 70, 1214).
Still another method involves spectrophotometric monitoring of a dye which is excluded from the gel in excess aqueous solution which becomes concentrated as the gel expands, as described in a Diploma Thesis by Herbert Heitmann, Universitat Dortmund Lehrstuhl fur Thermische Verfahrenstechnik, August 1989.
Each of these methods suffers from certain deficiencies. The vortex method has a subjective end point. This end point may also be unduly influenced by the presence of high molecular weight extractable components which can prematurely thicken the solution. The FSR method and the vortex method do not distinguish between fluid which is actually gelled and fluid which is loosely held interstitially, and thus can be easily expressed by pressure or capillary contact back onto the skin of the wearer. It is believed that a substantial fraction of the fluid (e.g., on the order of about 50% or more) at the FSR endpoint is held interstitially. It is further believed that the fraction of fluid held interstitially at the FSR endpoint will vary depending on particle morphology. Also, the FSR method is not usable for HFAPs which absorb the fluid very quickly as the apparent fluid uptake is achieved before all of the HFAP used in the test is wetted. The FSR method, like the vortex method, has an imprecise endpoint, which is particularly critical for very fast HFAPs. The spectrophotometric method, as described above, is not quickly responsive to changes in gel volume. Such a quick response requires minimal lag time between sampling and the reading of optical absorbency. This obviously becomes important for very fast HFAPs. Also, this method does not filter out floating pieces of small material generated during stirring which tend to interfere with the light path.
Applicants have modified the spectrophotometric method to provide data on the actual rate of gellation critical to the performance of an absorbent product. This was achieved by shortening the sampling path length to shorten the time between the actual change in optical absorbency and the spectrophotometric response to that change. Further, a self-cleaning filtration assembly was added to exclude particulate materials which can interfere with the light path. Unlike the vortex method supra, Applicants"" approach is not sensitive to extractable materials which may thicken the solution (but which do not change the optical absorbency of the solution). Unlike the vortex method and the Free Swell Rate method (supra), this modified method has a specific end point independent of operator judgment. Unlike the Free Swell and Vortex methods, this method does not measure trapped interstial fluid. Unlike the Free Swell Rate method (supra), this method is also usable for very fast HFAPs useful in the present invention.
The data obtained initially show optical absorbency which is simply converted into gel volume as a function of elapsed time. The data curves showing gel volume vs. elapsed time can be fit using a simple logarithmic expression defined hereinafter. This allows unambiguous expression of the gelling curve using a single value, referred to herein as the Dynamic Gelling Rate, or DGR, in units of g/g/sec. HFAPs which exhibit faster rates without compromising other properties unacceptably have been found to be particularly preferred in specific types of absorbent core designs, described in detail hereinafter.
It has been generally recognized as desirable to have the expressed fluid converted into the gelled state as rapidly as possible. For example, U.S. Pat. No. 5,439,458 (Noel et al.) issued Aug. 8, 1995 describes absorbent articles with a xe2x80x9crapid acquiring, multiple layer absorbent corexe2x80x9d using a xe2x80x9cxe2x80x9chigh-speedxe2x80x9d absorbent gelling material capable of reaching at least 40% of its absorbent capacity in less than or equal to about 10 seconds.xe2x80x9d U.S. Pat. No. 5,300,054 (Feist et al.) issued Apr. 5, 1994 describes absorbent cores having storage layers at least partially comprising high speed absorbent gelling material. High speed HFAPs generally have been disclosed. For example, U.S. Pat. No. 5,563,218 (Rebre et al.) issued Oct. 8, 1996 discloses a process for producing xe2x80x9chigh gel strength/short gel time acrylic polymersxe2x80x9d. U.S. Pat. No. 5,601,542 (Melius et al.) issued Feb. 11, 1997 describes absorbent composites having specified vortex times and demand gel volumes under pressure (infra). U.S. Pat. No. 5,149,335 (Kellenberger et al.) issued Sep. 22, 1992 describes use of superabsorbent material at least 15 g/g Absorbency Under Load (AUL) (infra) after 5 minutes and a Free Swell Rate of less than about 60 seconds.
U.S. Pat. No. 5,354,290 (Gross) issued Oct. 11, 1994 and U.S. Pat. No. 5,403,870 (Gross) issued Apr. 4, 1995 describe a method for producing porous HFAPs with high absorbent rates. U.S. Pat. No. 5,154,713 (Lind) issued Oct. 13, 1992, U.S. Pat. No. 4,649,164 (Scott et al.) issued Mar. 10, 1987, U.S. Pat. No. 4,529,739 (Scott et al.) issued Jul. 16, 1985, U.S. Pat. Nos. 5,154,714, and 5,399,591 describe inclusion of carbonate blowing agents in the HFAP manufacturing process to increase internal and external surface area and increase absorbent rates. World Patent 95/17,455 describes porous superabsorbents with high absorption rates generated by use of nitrogen generating initiators during the polymerization. World Patent Publication WO 96/17,884 published June, 1996, describes dispersal of solid blowing agent in the aqueous solution of monomer and crosslinker followed by heating to polymerize into a porous structure with a high rate of water absorption. The disclosure of this publication is incorporated herein by reference.
In some cases, use of high concentrations of fast HFAPs, particularly in the loading zone of the absorbent core, can actually impair fluid sorption rates. This is believed to result from rapid gellation of the HFAP with attendant tendencies to reduce porosity and/or permeability, and even gel block, and thus reduce the ability of the absorbent core to accommodate repeat insults of the body fluid. In such cases, it can be desirable to employ HFAPs with particularly high porosities and/or permeabilities so as to avoid this problem. Alternatively, a mixture of HFAP types can be employed wherein at least part of the HFAP blend has a very high rate of fluid uptake and porosity and/or permeability.
Other physical and chemical characteristics of these hydrogel-forming absorbent polymers are important to performance in absorbent structures. One characteristic is the particle size, and especially the particle size distribution, of the hydrogel-forming absorbent polymer used in the fibrous matrix. For example, particles of hydrogel-forming absorbent polymer having a particle size distribution such that the particles have a mass median particle size greater than or equal to about 400 xcexcm have been mixed with hydrophilic fibrous materials to minimize gel blocking and to help maintain an open capillary structure within the absorbent structure so as to enhance planar transport of fluids away from the area of initial discharge to the rest of the absorbent structure. Such larger particles tend to be relatively slow to imbibe aqueous fluids. While smaller particles of HFAP will generally show faster rates of gellation, this can also lead to depressed gel volumes (when surface crosslinker, infra) and/or gel blocking as a result of such small particles. Small particles in the dry state can also be difficult to handle in manufacturing due to problems with respirable dust. Small particles in this discussion refers to generally (compact) spherical (e.g., not cylindrical as is a fiber) materials which have a maximum cross-sectional dimension of about 100 xcexcm. Small particles, also called fines, may also be reformed into aggregates or agglomerates by additional processing (or by methods of preparation; e.g., suspension polymerization). This can minimize some of the problems associated with use of fines. However, the additional processing step can be problematic and expensive. Also, the agglomerated particles tend not to be stable during processing and usage and often release significant quantities of fines back into the absorbent product. Accordingly, it is preferred that the HFAPs useful herein not be in the form of agglomerated particles. That is, unagglomerated HFAPs are preferred herein. (FIG. 5 illustrates unagglomerated HFAP particles useful herein). Hydrogel-forming absorbent polymers useful herein can be derived from fines by impregnation with additional monomer to build up their size as described in U.S. Pat. No. 5,514,574 (Henderson et al.), issued May 7, 1996. U.S. Pat. No. 5,122,544 (Bailey et al.) issued Jun. 16, 1992 describes a process for agglomerating gel fines using difunctional epoxides. U.S. Pat. No. 4,950,692 (Lewis et al.) issued Aug. 21, 1990 and U.S. Pat. No. 4,970,267 (Bailey et al.) issued Nov. 13, 1990 similarly describe agglomeration of gel fines. U.S. Pat. No. 5,384,343 describes a process for agglomeration of fines ( less than 50 xcexcm into larger particles of 50-500 xcexcm). U.S. Pat. No. 5,369,148 (Takahashi et al.) issued Nov. 29, 1994 describes a method of agglomeration of absorbent resin powder. U.S. Pat. No. 5,455,284 (Dahmen et al.) issued Oct. 3, 1995 describes recycling fines into more monomer from which a new HFAP may be formed via polymerization. U.S. Pat. No. 5,248,709 (Brehm) issued Sep. 28, 1993 describes a method for sinter granulation of fines. U.S. Pat. No. 5,350,799 (Woodrum et al.) issued Sep. 27, 1994 describes yet another process for converting fines into large particles. French Patent 2,732,973 issued October 1996, describes a process to provide a good yield of aggregated particles without fines. The above references are incorporated herein by reference.
Another important characteristic is particle size distribution of the hydrogel-forming absorbent polymer. This can be controlled to improve absorbent capacity and efficiency of the particles employed in the absorbent structure. See U.S. Pat. No. 5,047,023 (Berg), issued Sep. 10, 1991, and U.S. Pat. No. 5,397,845 (Rebre et al.) issued Mar. 14, 1995 and U.S. Pat. No. 5,412,037 (Rebre et al.) issued May 2, 1995 describing HFAPs with a narrow particle size distribution between 100 and 500 xcexcm essentially devoid of fines. However, even adjusting the particle size distribution does not, by itself, lead to absorbent structures that can have relatively high concentrations of these hydrogel-forming absorbent polymers. See U.S. Pat. No. 5,047,023, supra (optimum fiber to particle ratio on cost/performance basis is from about 75:25 to about 90:10).
Another characteristic of these hydrogel-forming absorbent polymers that has been looked at is the level of extractables present in the polymer itself. See U.S. Pat. No. 4,654,039 (Brandt et al.), issued Mar. 31, 1987 (reissued Apr. 19, 1988 as U.S. Reissue Pat. No. 32,649). Many of these hydrogel-forming absorbent polymers contain significant levels of extractable polymer material. This extractable polymer material can be leached out from the resultant hydrogel by body fluids (e.g., urine) during the time period such body fluids remain in contact with the hydrogel-forming absorbent polymer. Such polymer material extracted by body fluid in this manner can alter the properties, e.g., increase viscosity and also electrolyte concentration of the body fluid to the extent that the fluid is more slowly absorbed and more poorly held by the hydrogel in the absorbent article.
Another important characteristic is the capillary capability of these hydrogel-forming absorbent polymers. In particular, it has been suggested that particles of these hydrogel-forming absorbent polymers be formed into interparticle crosslinked aggregate macrostructures, typically in the form of sheets or strips. See U.S. Pat. No. 5,102,597 (Roe et al.), issued Apr. 7, 1992; U.S. Pat. No. 5,124,188 (Roe et al.), issued Jun. 23, 1992; and U.S. Pat. No. 5,149,344 (Lahrman et al.), issued Sep. 22, 1992. Because the particulate nature of the absorbent polymer is retained, these macrostructures provide pores between adjacent particles that are interconnected such that the macrostructure is fluid permeable (i.e., has capillary transport channels).
Another important characteristic is gel blocking as measured in a Demand Wettability or Gravimetric Absorbence test. See, for example, U.S. Pat. No. 5,147,343 (Kellenberger), issued Sep. 15, 1992 and U.S. Pat. No. 5,149,335 (Kellenberger et al.), issued Sep. 22, 1992 where these hydrogel-forming absorbent polymers are referred to as xe2x80x9csuperabsorbent materialsxe2x80x9d and where Demand Wettability/Gravimetric Absorbence is referred to as Absorbency Under Load (AUL). xe2x80x9cAULxe2x80x9d is defined in these patents as the ability of the hydrogel-forming absorbent polymer to swell against an applied restraining force (see U.S. Pat. No. 5,147,343, supra, at Col. 2, lines 43-46). The xe2x80x9cAUL valuexe2x80x9d is defined as the amount (in mL/g or g/g) of 0.9% saline solution that is absorbed by the hydrogel-forming absorbent polymers while being subjected to a load of 21,000 dynes/cm2 (about 0.3 psi). The AUL value can be reported after 1 hour (see U.S. Pat. No. 5,147,343) or 5 minutes (see U.S. Pat. No. 5,149,335). Hydrogel-forming absorbent polymers are deemed to have desirable AUL properties if they absorb at least about 24 mL/g (preferably at least about 27 mL/g) of the saline solution after 1 hour (see U.S. Pat. No. 5,147,343) or at least about 15 g/g (preferably at least about 18 g/g) of the saline solution after 5 minutes.
AUL as defined in U.S. Pat. Nos. 5,147,343 and 5,149,335 may provide some indication of which hydrogel-forming absorbent polymers will avoid gel blocking in some instances. However, AUL does not specifically determine rate of gelling or distinguish between moderately fast and very fast absorbing HFAPs. Further, AUL is inadequate for determining which hydrogel-forming absorbent polymers will provide the absorbency properties necessary for high concentration absorbent cores, as is described in U.S. Pat. No. 5,599,335 (supra). In particular, using AUL values measured according to U.S. Pat. Nos. 5,147,343 and 5,149,335 is inadequate in that they do not reflect all of the potential pressures that can be operative on the hydrogel-forming polymer in the absorbent structure. As noted above, AUL is measured in these patents at a pressure of about 0.3 psi. It is believed that a much higher confining pressure of about 0.7 psi more adequately reflects the full range of localized mechanical pressures (e.g., sitting, sleeping, squatting, taping, elastics, leg motions, other tension and torsional motions) on an absorbent structure. See U.S. Pat. No. 5,147,345 (Young et al), issued Sep. 15, 1992. Additionally, many of the absorbent structures that comprise these hydrogel-forming absorbent polymers can include other components, such as an acquisition layer that receives the initial discharge of body fluids. See, for example, U.S. Pat. No. 4,673,402 (Weisman et al), issued Jun. 16, 1987 and U.S. Pat. No. 4,935,022 (Lash et al), issued Jun. 19, 1990. This acquisition layer can comprise fibers, such as certain chemically stiffened fibers, that have a relatively high capillary suction. See, for example, U.S. Pat. No. 5,217,445 (Young et al), issued Jun. 8, 1993. To take into account these additional capillary pressures that could affect fluid acquisition by these hydrogel-forming absorbent polymers, it is more realistic to measure demand absorbency performance under a higher pressure, i.e., about 0.7 psi. This takes into better account not only the localized mechanical pressures exerted during use, but also the additional capillary pressures resulting from other components (e.g., acquisition layer) present in the absorbent structure. See U.S. Pat. No. 5,599,335 (Goldman et al.), which incorporated by reference herein, which describes a means for measuring demand absorbency under such higher pressures.
Pressure Absorbency Index (PAI) is defined in U.S. Pat. No. 5,601,542 (issued Feb. 11, 1997) Melius et al. as the sum of the AUL values determined at four pressures (0.01 psi, 0.29 psi, 0.57 psi, and 0.90 psi). This is another way of presenting AUL data as an aggregate to include the effects of pressure on AUL.
Still other characteristics for absorbent structures having relatively high concentrations of these hydrogel-forming absorbent polymers have been evaluated. See, for example, European patent application 532,002 (Byerly et al.), published Mar. 17, 1993, which identifies a characteristic called Deformation Under Load (DUL) as being important for absorbent composites having high concentrations of hydrogel-forming absorbent polymers. xe2x80x9cDULxe2x80x9d is used in European patent application 532,002 to evaluate the ability of the hydrogel-forming absorbent polymer to maintain wicking channels after the absorbent polymer is swollen. See page 3, lines 9-10. Further discussion of the DUL method may be found in U.S. Pat. No. 5,562,646 (supra). U.S. Pat. No. 5,562,646 describes hydrogel-forming absorbent polymers having higher porosities that are particularly suitable for absorbent structures having high concentrations of these absorbent polymers. The openness or porosity of a hydrogel layer formed from a hydrogel-forming absorbent polymer can be defined in terms of Porosity of the Hydrogel Layer (PHL). A good example of a material having a very-high degree openness is an air-laid web of wood-pulp fibers. For example, the fractional degree of openness of an air-laid web of wood pulp fibers (e.g., having a density of 0.15 g/cc) is estimated to be 0.8-0.9, when wetted with body fluids under a confining pressure of 0.3 psi. By contrast, typical hydrogel-forming polymers such as Nalco 1180 (made by Nalco Chemical Co.) and L-761f (made by Nippon Shokubai Co., LTD) exhibit PHL values of about 0.1 or less
U.S. Pat. No. 5,562,646 teaches that higher PHL values for the hydrogel-forming absorbent polymer can provide benefits in high concentration cores including (1) increased void volume in the resultant hydrogel layer for acquiring and distributing fluid; (2) increased total quantity of fluid absorbed by the absorbent polymer under demand wettability/gravimetric absorbency conditions (i.e., for the storage of fluid); (3) increased permeability of the resultant hydrogel layer for acquiring and distributing fluid; (4) improved wicking properties for the resultant hydrogel layer, such as wicking fluid upwardly against gravitational pressures or partitioning fluid away from an acquisition layer; and (5) improved swelling-rate properties for the resultant hydrogel layer to allow more-rapid storage of fluid.
U.S. Pat. No. 5,599,335 teaches the importance in cores having higher concentrations of these hydrogel-forming absorbent polymers is their permeability/flow conductivity. Permeability/flow conductivity can be defined in terms of their Saline Flow Conductivity (SFC) values. SFC measures the ability of a material to transport saline fluids, such as the ability of the hydrogel layer formed from the swollen hydrogel-forming absorbent polymer to transport body fluids. Typically, an air-laid web of pulp fibers (e.g., having a density of 0.15 g/cc) will exhibit an SFC value of about 200xc3x9710xe2x88x927 cm3sec/g. By contrast, typical hydrogel-forming absorbent polymers such as Aqualic L-74 (made by Nippon Shokubai Co., LTD) and Nalco-1180 (made by Nalco Chemical Co.) exhibit SFC values of generally less than 1xc3x9710xe2x88x927 cm3sec/g. Accordingly, it would be highly desirable to be able to use hydrogel-forming absorbent polymers that more closely approach an air-laid web of wood pulp fibers in terms of SFC. HFAPs having relatively high SFC values are particularly important wherein the relatively fast HFAPs of the present invention are used in the loading zone in high concentrations.
It is obvious from this discussion that no single parameter associated with HFAPs can be defined or measured to describe the suitability of a given HFAP for a given high concentration absorbent core design. Heretofore unrecognized is the importance of rate of gellation of the HFAP in concert with their ability to absorb fluid against a confining pressure.
Accordingly, it would be desirable to be able to provide an absorbent member comprising: (1) a region or regions having a relatively high concentration of hydrogel-forming absorbent polymer; (2) using HFAPs with very fast rates of gellation; (3) with relatively large particle sizes or fiber sizes; (4) that can readily acquire fluids under typical usage pressures (e.g., 0.7 psi); preferably (5) with relatively high porosities, especially when used in the loading zone, and preferably (6) permeability/flow conductivity properties more like an air-laid fibrous web.
The present invention relates to absorbent members useful in the containment of body fluids such as urine and blood. These absorbent members comprise at least one region having hydrogel-forming absorbent polymer in a concentration of from about 50 to 100% by weight. This hydrogel-forming absorbent polymer has:
(a) a Performance under Pressure (PUP) capacity value of at least about 25 g/g under a confining pressure of 0.7 psi (5 kPa);
(b) a Dynamic Gelling Rate (DGR) value of at least about 0.18 g/g/sec; and
(c) when the hydrogel-forming absorbent polymer is in the form of particles, a mass median particle size of at least about 100 xcexcm.